Steven Newman, left, of Transocean Limited, Lamar McKay, of BP America, Inc., Timothy Probert, of Global Business Lines and Jack Moore, of Cameron, are sworn in before they testify during a House subcommittee hearing on the Gulf Coast oil spill on Wednesday on Capitol Hill in Washington.

By Alan Levin, USA TODAY

WASHINGTON  Emergency shut-off valves that could have prevented the Gulf of Mexico oil spill were plagued by leaking hydraulic fluid, malfunctioning parts and poor maintenance, Congressional investigators said Wednesday.

The problems with the blowout preventer on the Deepwater Horizon drilling rig could explain why it failed April 20, allowing a spout of oil and gas to explode and kill 11 workers, according to documents released by the House energy committee's Oversight and Investigations Subcommittee.

"The safety of its entire operations rested on the performance of a leaking, modified, defective blowout preventer," said Rep. Bart Stupak, D-Mich., chairman of the subcommittee.

House investigators also revealed that the well had failed at least two pressure tests in the hours before it blew, raising questions about whether cement recently poured into the well could hold back the high-pressure oil and gas.

"The more I learn about this accident, the more concerned I become," said Rep. Henry Waxman, D-Calif., Energy and Commerce Committee chairman.

Evidence about precisely what happened on the rig remains "murky," Waxman said, but the committee released the most detailed account to date.

The blowout preventer, a massive device that sits atop the well opening on the floor of the Gulf, was activated by the crew aboard the floating drill rig as the emergency unfolded. But the preventer did not stop the surge.

In the days after the explosion, crews operating underwater robots tried again to activate the blowout preventers. However, they discovered that there was a "significant leak" of the hydraulic fluid, Stupak said. The fluid is meant to activate a part of the blowout preventer designed to shut off oil in an emergency.

Employees of Cameron, which manufactured the blowout preventer, told the committee the leak was coming from a loose connection, Stupak said.

Blowout preventers are equipped with a variety of different valves that can help shut off a sudden surge. Only after the accident did workers discover that one of those valves had been replaced by testing equipment that was "useless," Stupak said.

A host of other problems may have interfered with the emergency shut-off system, Stupak said. At least one battery used to trigger a critical valve used in emergencies was dead, he said.

A 2001 document obtained by the committee from Transocean, the drilling company that owned the rig, identified 260 separate ways that the blowout preventer could fail. "How can a device that has 260 failure modes be considered fail-safe?" Stupak said.

Steven Newman the CEO of Transocean told the committee that crews had not seen evidence of problems in tests prior to the accident.

Energy giant BP, which owns the well and had hired Transocean, said it relied on the blowout preventer to ensure safety. "We do expect those to work, absolutely," said BP America's Chairman Lamar McKay.

To report corrections and clarifications, contact Standards Editor Brent Jones. For publication consideration in the newspaper, send comments to letters@usatoday.com. Include name, phone number, city and state for verification. To view our corrections, go to corrections.usatoday.com.

Guidelines: You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. Read more.